8 research outputs found
Effect of impurities on morphology and growth mode of (111) and (001) epitaxial-like ScN films
ScN material is an emerging semiconductor with an indirect bandgap. It has
attracted attention for its thermoelectric properties, use as seed layers, and
for alloys for piezoelectric application. ScN or other transition metal nitride
semiconductors used for their interesting electrical properties are sensitive
to contaminants, such as oxygen or fluorine. In this present article, the
influence of depositions conditions on the amount of oxygen contaminants
incorporated in ScN films were investigated and their effects on the electrical
properties (electrical resistivity and Seebeck coefficient) were studied. The
epitaxial-like films of thickness 125 +-5 nm to 155 +-5 nm were deposited by
D.C.-magnetron sputtering on c-plane Al2O3, MgO(111) and r-plane Al2O3 at a
substrate temperature ranging from 700 to 950 degree C. The amount of oxygen
contaminants presents in the film, dissolved into ScN or as an oxide, was
related to the adatom mobility during growth, which is affected by the
deposition temperature and the presence of twin domain growth. The lowest
values of electrical resistivity of 50 micro-ohm cm were obtained on
ScN(111)/MgO(111) and on ScN(001)/r-plane Al2O3 grown at 950 degree C with no
twin domains and the lowest amount of oxygen contaminant. At the best, the
films exhibited an electrical resistivity of 50 micro-ohm cm with Seebeck
coefficient values maintained at -40 microV K-1, thus a power factor estimated
at 3.2 10-3 W m-1 K-2 (at room temperature)
Reduction of the thermal conductivity of the thermoelectric material ScN by Nb alloying
ScN-rich (Sc,Nb)N solid solution thin films have been studied, motivated by the promising thermoelectric properties of ScN-based materials. Cubic Sc1-xNbxN films for 0 amp;lt;= x amp;lt;= 0.25 were epitaxially grown by DC reactive magnetron sputtering on a c-plane sapphire substrate and oriented along the (111) orientation. The crystal structure, morphology, thermal conductivity, and thermoelectric and electrical properties were investigated. The ScN reference film exhibited a Seebeck coefficient of -45 mu V/K and a power factor of 6 x 10(-4) W/m K-2 at 750K. Estimated from room temperature Hall measurements, all samples exhibit a high carrier density of the order of 10(21) cm(-3). Inclusion of heavy transition metals into ScN enables the reduction in thermal conductivity by an increase in phonon scattering. The Nb inserted ScN thin films exhibited a thermal conductivity lower than the value of the ScN reference (10.5W m(-1) K-1) down to a minimum value of 2.2 Wm(-1) K-1. Insertion of Nb into ScN thus resulted in a reduction in thermal conductivity by a factor of similar to 5 due to the mass contrast in ScN, which increases the phonon scattering in the material. Published by AIP Publishing.Funding Agencies|European Research Council under the European Community [335383]; Swedish Foundation for Strategic Research (SSF) through the Future Research Leaders 5 program; Swedish Research Council (VR) [621-2012-4430, 2016-03365]; Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows program; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; project NanoCaTe (FP7-NMP) [604647]; project CTEC [1305-00002B]</p
Effect of ion-implantation-induced defects and Mg dopants on the thermoelectric properties of ScN
For applications in energy harvesting, environmentally friendly cooling, and
as power sources in remote or portable applications, it is desired to enhance
the efficiency of thermoelectric materials. One strategy consists of reducing
the thermal conductivity while increasing or retaining the thermoelectric power
factor. An approach to achieve this is doping to enhance the Seebeck
coefficient and electrical conductivity, while simultaneously introducing
defects in the materials to increase phonon scattering. Here, we use Mg ion
implantation to induce defects in epitaxial ScN (111) films. The films were
implanted with Mg+ ions with different concentration profiles along the
thickness of the film, incorporating 0.35 to 2.2 at.% of Mg in ScN.
Implantation at high temperature (600 C), with few defects due to the
temperature, does not substantially affect the thermal conductivity compared to
a reference ScN. Samples implanted at room temperature, in contrast, exhibited
a reduction of the thermal conductivity by a factor of three. The sample doped
with 2.2 at.% Mg also showed an increased power factor after implantation. This
study thus shows the effect of ion-induced defects on thermal conductivity of
ScN films. High-temperature implantation allows the defects to be annealed out
during implantation, while the defects are retained for room-temperature
implanted samples, allowing for a drastic reduction in thermal conductivity.Comment: Main manuscript: 22 pages, 7 figures Supplemental information: 10
pages, 10 figure
Review of Spark Discharge Generators for Production of Nanoparticle Aerosols
In the growing field of nanotechnology there is an increasing need to develop production methods for nanoparticles, especially methods that provide control and reproducibility. The spark discharge generator (SDG) is a versatile device for the production of nanoparticle aerosols. It can produce aerosol nanoparticles in the entire nanometer range (1-100 nm), and beyond. Depending on requirements, and the system used, these nanoparticles can be completely contamination free and composed of one or more materials. This provides a unique opportunity to create new materials on the nanoscale. Already in use in semiconductor, materials, health and environmental research, the SDG shows promise for yet more applications. If needed, particle production by the SDG could be scaled up using parallel generators facilitating continuous high-volume production of aerosol nanoparticles. Still, there is a surprisingly low knowledge of fundamental processes in the SDG. In this article we present a thorough review of the most common and relevant SDGs and the theory of their operation. Some possible improvements are also discussed